It is known to construct an acoustic charge transport (ACT) delay line using a SAW transducer to launch an acoustic wave through a piezoelectric slab semiconductor. FIG. 2 illustrates a sketch of one such prior art device, in which GaAs layer 10 carries the SAW and layer 10 is positioned above a thick substrate layer 20, also of GaAs. Vertical charge confinement is provided by electrodes 150 and 160 with voltages V.sub.A and V.sub.B applied.
FIG. 3 illustrates another prior art device, a heterostructure acoustic charge transport (HACT) device, in which the charge transport channel 225 corresponding to channel 10 in FIG. 2, is sandwiched between two layers 230 and 220 of (Al,Ga)As. This last device, illustrated in U.S. Pat. No. 4,893,161, uses the semiconductor band structure properties of upper and lower confinement or barrier layers to provide vertical charge confinement.